Imaging Method for Use in Surgical Procedures

ABSTRACT

Apparatus for imaging during surgical procedures includes an operating room for the surgical procedure and an MRI for obtaining images periodically through the surgical procedure by moving the magnet up to the table. The magnet wire is formed of a superconducting material such as magnesium di-boride or Niobium-Titanium which is cooled by a vacuum cryocooling system to superconductivity without use of liquid helium. The magnet weighs less than 1 to 2 tonne and has a floor area in the range 15 to 35 sq feet so that it can be carried on the floor by a support system having an air cushion covering the base area of the magnet having side skirts so as to spread the weight over the entire base area. The magnet remains in the room during surgery and is powered off to turn off the magnetic field when in the second position remote from the table.

This application claims the benefit under 35 USC 119 (e) of Provisionalapplications 62/799,498 and 62/799,510 both filed Jan. 31, 2019.

This invention relates to a movable MRI system for use in surgicalprocedures.

BACKGROUND OF THE INVENTION

Magnetic resonance imaging (MRI) is a non-invasive imaging modalitycapable of distinguishing a wide variety of objects based on theirintrinsic composition and also is an imaging technique that is capableof providing one-, two- or three-dimensional imaging of the object. Aconventional MRI system typically includes a main or primary magnet thatprovides the main static magnetic field, B0, magnetic field gradientcoils and radio frequency (RF) coils, which are used for spatialencoding, exciting and detecting the nuclei for imaging. Typically, themain magnet is designed to provide a homogeneous magnetic field in aninternal region within the main magnet, for example, in the air space ofa large central bore of a solenoid or in the air gap between themagnetic pole plates of a C-type magnet. The patient or object to beimaged is positioned in the homogeneous field region located in such airspace. The gradient field used to convert distance into frequency andthe RF coils used to transmit and receive signals from the patient aretypically located external to the patient or object to be imaged andinside the geometry of the main or primary magnet(s) surrounding the airspace.

Typically the uniform magnetic field B0 generated by the main magnet onthe high field MRI systems (>1.0 Tesla) is generated and then remains onfor the life of the magnet, although the field maybe boosted every nowand then during the magnet's operating life. In conventional MRIdevices, the patient is bought to the magnet, placed on a patient couchand then slid into the magnet with the region to be imaged placed asclose to the isocenter of the magnet. This requires that the patient beeither ambulatory or can be brought to the magnet on a gurney and slidinto the magnet. There are many times when the physician would prefer tobring the MRI magnet to the patient since the patient is in a positionwhere he/she should not be moved. Examples include patient undergoingsurgical or interventional procedures where the physician needs an imageor for patients such as stroke or accident victims who by theircondition should not be moved.

Modern neurosurgery encompasses the surgical treatment of many complexconditions such as primary intracranial or spinal neoplasms, lesions ofthe cranium and cranial base, cerebral vascular disorders includingarteriovenus malformations, cavernous angiomas and intracranialaneurysms, and inflammatory conditions. Concurrent with these changes,imaging by computerized tomography, magnetic resonance, positronemission tomography, and magnet wave processing provide greatly improvedcomprehension of brain structure and functional events. Imaging datahave been incorporated into stereotactic space by a number of devices toallow a precise point access and volume comprehension for planning andtrans-cerebral navigation, all with striking reduction in operativeworking corridor size. However, this imaging technology needs to betaken to the operating theatre so that changes that result from brainshift and tissue removal and the extent of surgical procedure can beaccommodated. A number of surgical intraoperative MRI devices have beendeveloped with the most popular being that sold by IMRIS. The challengewith this IMRIS device is that the installation requires extensiverenovations to the hospital operating theatre which is very expensiveand results in the operating theatre being unavailable for a significantperiod of time.

SUMMARY OF THE INVENTION

According to one aspect of the invention which can be used independentlyof other features set out herein there is provided an apparatus for usein surgical procedures comprising:

an operating room having a floor and walls containing an operating tablefor receiving a patient for a surgical procedure;

and a magnetic resonance imaging system for obtaining images of a partof the patient at a series of times through the surgical procedure foranalysis by the surgical team to allow the surgical team to monitor theprogress of the surgery, the magnetic resonance imaging systemcomprising:

a magnet system comprising a cylindrical magnet of magnet wire defininga cylindrical bore within which a part of the patient is located forplacement within high magnetic fields generated by the magnet;

a control system for controlling and varying the magnetic fields;

a radio frequency transmission and detection system for eliciting anddetecting from the part of the patient nuclear magnetic resonancesignals, in response to the magnetic field, including an RF probearranged to be located adjacent to the part of the patient;

and a computer and display monitor for decoding and displaying thedetected signals;

a table support system mounting the magnet for movement relative to thetable in a direction away from the first end of the table from a firstposition at the table to a second position remote from the table;

the first position of the magnet being arranged such that the part ofthe patient is positioned in the magnetic field of the magnet while thepatient remains in place on the table;

the second position of the magnet being arranged such that the magnet isspaced from the first end of the table by a distance sufficient to allowthe surgical team to move around the first end of table and to each sideof the table to access the patient and sufficient to allow to allow thesurgical team to carry out the surgical procedure;

wherein the magnet wire is formed of a superconducting material which iscooled by a cooling system to superconductivity without use of liquidhelium.

Preferably the magnet wire is formed from magnesium di-boride whichrequires a temperature of around 40 degrees absolute which can bereached without use of liquid helium and typically using a vacuumcryo-cooling system having a vacuum pump. Other materials which can beused are Niobium Titanium and, possibly although less suitably,Niobium-Tin.

For example, using these techniques, the magnet can have a weight ofless than 2 tonne and a floor area in the range 15 to 40 sq feet andtypically around 35 sq feet which can be tolerated by most standardfloor systems.

This allows preferably the magnet to be carried on a support systemsupported from the floor. In particular the support system can comprisean air cushion covering the base area of the magnet having side skirtsso as to spread the weight over the entire base area. In order to beused in an operating theater, preferably the air cushion system isarranged so that it expels no particles from the side skirts.

While the magnet preferably floats on the air cushion to spread theload, preferably the support system is guided from the first position tothe second position on guide rails.

In another preferred arrangement, the magnet is carried on a pair ofside tracks in the manner of a skid steer loader so that the side tracksalong the sides of the magnet base carry the weight and can becontrolled sufficiently accurately to drive the magnet forward intoposition relative to the table. It will be appreciated that the magnetbore just fits along the table so that the accuracy of drive must bevery high to ensure the required proper location of the magnet withoutthe use of guide rails.

As explained in more detail hereinafter, also the tracks allow themagnet to be rotated about a vertical axis at or adjacent a center ofthe magnet so as to move a forward end of the magnet into a room in therequired orientation.

An arrangement of this type can preferably allow the magnet to bepowered off to turn off the magnetic field when in the second position.In this way the magnet can sit dormant in the same room as the operatingprocedure but preferably with the cooling system remaining on when themagnetic field is powered off. In this arrangement preferably the magnetdedicated solely to surgery within the operating room and remains in theroom. Even though cost can be shared by multi-uses of the magnet, inthis arrangement, the small construction of the magnet allowing it to besupported from the floor and the simple connection of the magnet to thecooling water and electrical supply allows it to be stalled in a verycost-effective manner. At the same time the magnet selected can providemore than 1 tesla which is sufficient to provide effective imaging.

To keep the weight down, the magnet has preferably a minimum borediameter of the order of 60 to 70 cms, typically around 65 cms, and alength in the range 5 feet.

Again to maintain the overall dimensions as small as possible, in somecases the RF probe comprises local transceiver RF coils so as to avoiduse of a cylindrical body coil at the bore which would otherwiseincrease the diameter of the magnet. However in other cases a body coilcan be used within the bore particularly as a transmit coil with thereceive coil being provided as a separate component particularly aroundthe head.

In order to avoid shielding the whole room as it typically required fromstray RF signals, preferably there is provided a shielding structure forexcluding RF fields from the RF probe which comprises an arched supportframe for extending over the patient and supporting a shielding fabricor screen material extending from the feet up to the location on thebody which enters the bore, a metal sheet as part of the table locatedunderneath the patient and extending across the table to the sides ofthe shielding fabric, a cylindrical shielding layer inside the bore anda hinged door on an end of the bore opposite the table and containing ashielding layer. The shielding material can be a screen materialencapsulated in a plastics material so as to form a stiff structurewhich retains its shape as an arch when deployed over the patient on thetable.

According to one aspect of the invention which can be used independentlyof other features set out herein there is provided an apparatus for usein surgical procedures comprising:

an operating room having a floor and walls containing an operating tablefor receiving a patient for a surgical procedure;

and a magnetic resonance imaging system for obtaining images of a partof the patient at a series of times through the surgical procedure foranalysis by the surgical team to allow the surgical team to monitor theprogress of the surgery, the magnetic resonance imaging systemcomprising:

a magnet system comprising a cylindrical magnet of magnet wire defininga cylindrical bore within which a part of the patient is located forplacement within high magnetic fields generated by the magnet;

a control system for controlling and varying the magnetic fields;

a radio frequency transmission and detection system for eliciting anddetecting from the part of the patient nuclear magnetic resonancesignals, in response to the magnetic field, including an RF probearranged to be located adjacent to the part of the patient;

and a computer and display monitor for decoding and displaying thedetected signals;

a table support system mounting the magnet for movement relative to thetable in a direction away from the first end of the table from a firstposition at the table to a second position remote from the table;

the first position of the magnet being arranged such that the part ofthe patient is positioned in the magnetic field of the magnet while thepatient remains in place on the table;

the second position of the magnet being arranged such that the magnet isspaced from the first end of the table by a distance sufficient to allowthe surgical team to move around the first end of table and to each sideof the table to access the patient and sufficient to allow to allow thesurgical team to carry out the surgical procedure;

wherein the magnet wire is formed from magnesium di-boride orNiobium-Titanium.

According to one aspect of the invention which can be used independentlyof other features set out herein there is provided an apparatus for usein surgical procedures comprising:

an operating room having a floor and walls containing an operating tablefor receiving a patient for a surgical procedure;

and a magnetic resonance imaging system for obtaining images of a partof the patient at a series of times through the surgical procedure foranalysis by the surgical team to allow the surgical team to monitor theprogress of the surgery, the magnetic resonance imaging systemcomprising:

a magnet system comprising a cylindrical magnet of magnet wire defininga cylindrical bore within which a part of the patient is located forplacement within high magnetic fields generated by the magnet;

a control system for controlling and varying the magnetic fields;

a radio frequency transmission and detection system for eliciting anddetecting from the part of the patient nuclear magnetic resonancesignals, in response to the magnetic field, including an RF probearranged to be located adjacent to the part of the patient;

and a computer and display monitor for decoding and displaying thedetected signals;

a table support system mounting the magnet for movement relative to thetable in a direction away from the first end of the table from a firstposition at the table to a second position remote from the table;

the first position of the magnet being arranged such that the part ofthe patient is positioned in the magnetic field of the magnet while thepatient remains in place on the table;

the second position of the magnet being arranged such that the magnet isspaced from the first end of the table by a distance sufficient to allowthe surgical team to move around the first end of table and to each sideof the table to access the patient and sufficient to allow to allow thesurgical team to carry out the surgical procedure;

wherein the magnet has a weight of less than 2 tonne and a floor area inthe range 15 to 40 sq feet and typically of the order of 35 sq feet andthe magnet is carried on a support system supported from the floor.

According to one aspect of the invention which can be used independentlyof other features set out herein there is provided a method for use insurgical procedures comprising:

providing an operating room having a floor and walls containing anoperating table for receiving a patient for a surgical procedure;

mounting in the room a magnetic resonance imaging system for obtainingimages of a part of the patient at a series of times through thesurgical procedure for analysis by the surgical team to allow thesurgical team to monitor the progress of the surgery, the magneticresonance imaging system comprising:

-   -   a magnet system comprising a cylindrical magnet of magnet wire        defining a cylindrical bore within which a part of the patient        is located for placement within high magnetic fields generated        by the magnet;    -   a control system for controlling and varying the magnetic        fields;    -   a radio frequency transmission and detection system for        eliciting and detecting from the part of the patient nuclear        magnetic resonance signals, in response to the magnetic field,        including an RF probe arranged to be located adjacent to the        part of the patient;    -   and a computer and display monitor for decoding and displaying        the detected signals;

mounting the magnet for movement relative to the table in a directionaway from the first end of the table from a first position at the tableto a second position remote from the table;

the first position of the magnet being arranged such that the part ofthe patient is positioned in the magnetic field of the magnet while thepatient remains in place on the table;

the second position of the magnet being arranged such that the magnet isspaced from the first end of the table by a distance sufficient to allowthe surgical team to move around the first end of table and to each sideof the table to access the patient and sufficient to allow to allow thesurgical team to carry out the surgical procedure;

wherein the magnet dedicated solely to surgery within the operatingroom;

wherein the magnet remains in the room at all times;

wherein the magnet is powered off to turn off the magnetic field when inthe second position;

and wherein the magnet is cooled by a cooling system which remains onwhen the magnetic field is powered off.

Magnets attract ferromagnetic material and products built with thesematerials can become projectiles when close to an MRI magnet and so themoveable magnet should only generate a magnetic field when required forimaging and spend the rest of its time with a magnetic field of around 0Tesla. The arrangement of the present invention allows the magneticfield to be turned off when the system is not being used for imaging.

Also if the magnet is to be moved, the present arrangement allows thatthe magnet not contain liquid helium since the use of liquid heliumrequires a quench pipe to be attached to the magnet because largeamounts of helium gas escape very rapidly from the magnet in the eventof a quench. Such a large amount of helium gas escaping into the imagingroom is dangerous and should not be allowed to occur. Thus the presentarrangement avoids the use of an insulated tube attached to the magnetto carry all the helium gas to the exterior of the building should suchan event occur. The present arrangement thus allows a system whichavoids the use of liquid helium as a coolant.

The quality of the image produced by the MRI techniques is dependent, inpart, upon the strength of the magnetic resonance (MR) signal receivedfrom the precessing nuclei. For this reason an independent RF coil isplaced in close proximity to the region of interest of the imagedobject, more particularly on the surface of the imaged object, as localcoils or surface coils in order to improve the strength of the receivedsignal. These coils receive the signals from the tissue.

The present arrangement allows the use of a surface coil of the typedescribed in U.S. Pat. No. 4,825,162 which shows a surface coil(s) foruse in MRI/NMRI imaging and methods related thereto. In the preferredembodiment of that invention, each surface coil is connected to theinput of an associated one of a like plurality of low-input-impedancepreamplifiers, which minimizes the interaction between any surface coiland any other surface coils not immediately adjacent thereto. Thesesurface coils can have square, circular and the like geometries. Thisyields an array of a plurality of closely spaced surface coils, eachpositioned so as to have substantially no interaction with all adjacentsurface coils. A different MR response signal is received at eachdifferent one of the surface coils from an associated portion of thesample enclosed within the imaging volume defined by the array. Eachdifferent MR response signal is used to construct a different one ofplurality of different images from each surface coil. These images arethen combined, on a point-by-point basis to produce a single compositeMR image of a total sample portion comprised of the MR response signalsfrom the entire array of surface coils.

The arrangement of the present invention allows the use of a surfacecoil as both a transmit and receive coil thus avoiding the use of aconventional body coil used in the majority of high field MRI systemsfor excitation (called transmit coils) located as a cylindricalstructure just inside the bore. These coils take up space in the magnetat a position inside the cylindrical gradient coils and thereforerequire the magnet bore to be about 10 cm larger in diameter than ifthis body coil was not present. This larger diameter magnet requiressignificantly more wire to make a homogeneous magnet resulting in a muchheavier magnet making floor loading much more of an issue.

It should be recognized that it is contemplated that the MRI methods ofthe present invention are to be used in connection with the performanceof clinical, diagnostic, interventional, and/or surgical procedures.Thus, it is contemplated and within the skill of those in the art toadapt the MRI methods of the present invention when needed toaccommodate the performance of such clinical, diagnostic,interventional, and/or surgical procedures.

However the arrangement herein is designed to be maintained continuallyin the room to which it is allocated which is typically an operatingtheater for neurosurgery but can be for other surgeries or can be adiagnostic suite. The MRI magnet in this invention is a 1 Tesla or moremagnet made from Magnesium Diboride (MgB2) or Niobium-Tin or NiobiumTitanium wire which is a high temperature super conducting wire (Tc isequal to or less than 400K). This high superconducting temperature(Tc=40 K), means that MgB2-based systems can be cooled by moderncryo-cooling devices, without the costly, problematic and hazardous useof liquid helium. The magnet will therefore not need a quench pipe to beconnected and so will be much more mobile than any conventional MRImagnet. The magnet can be taken in 10 to 15 minutes to provide a stablehomogeneous magnetic field sufficient for high quality MRI imaging. Thefield is stabilized using control currents which are applied to themagnet wire in response to detection of the field to cause a rapidstabilization.

Therefore the magnet can spend all the time when not imaging at a nearzero field and is activated by application of the current to provide themagnetic field when required for imaging. Such a magnet is 70 to 80 cmin internal diameter and weighs less than 2 tonne and so can be movedaround a hospital floor using an air cushion or track support systemwith a standard or conventional floor without extra strengthening beingable to accept the necessary loading. The magnet transport system whenusing an air cushion is constructed such that no particles escape fromthe skirts designed to stop all particles from entering the hospitalatmosphere.

The RF coils will be of the transceiver design with the structure beingmalleable to form the required actual design to match the body regionrequired to be imaged. The RF transceiver can thus be formed of aflexible structure such as a fabric containing the coils or loopswithout necessity for any stiffening components to hold the structure ata required location allowing the structure to drape over the imagingarea. The structure is arranged to be located at or around theconventional head clamp used in the neurosurgery.

This is not a device normally required to perform whole body imaging butdesigned to image a particular body region with high resolution and highsensitivity. The coil as a receive coil has many channels, the numberdepending on the body region to be imaged and the signals from eachelement will be summed to provide the required image. These receivechannels are switched so that they are all connected for the RF transmitprocess to excite all the hydrogen nuclei in the tissue of interest.

For imaging during normal neurosurgical procedures, the magnet isbrought over the patient as has been described previously.

For deep brain stimulation and other procedures on the brain performedby neurosurgeons, the magnet is powered down to zero field and thesystem is moved so that the magnet is located over the chest and thestomach of the patient. This leaves the head of the patient exposedbeyond the end of the magnet remote from the table. The surgeon startsthe surgical procedures which require the use of ferromagnetic materialswhich are attracted to the magnet if at non-zero field. Typically, thisis used to form burr holes in the skull using drilling tools. Thus, thesurgeon can use conventional tools to carry out the conventionalsurgical procedures without danger from the attraction to the magnet.

When this part of the procedure is completed, the magnet is turned onand the surgeon can continue the procedure but using only MRI safedevices. The completion of these tasks requires supports in place forthe introduction of one or two insertion cannulas or electrodes throughthe burr holes which have been made in the patient's skull in the firstpart of the procedure. The trajectory of these are based on stereotacticimaging. When the magnet is at field, relative movement of the patientand magnet is provided such that the head of the patient is receivedinto the homogeneous field of view of the magnet. This can be obtainedby the longitudinal movement of the magnet along the table on its movingsystem. In an alternative embodiment, a telescopic component of thepatient table is moved to place the patient's head in the imaging fieldof view. Images are obtained and fused with pre-operative images whichmay contain anatomical, functional, and tractography information. Theseimages are used to verify that the trajectory for the electrodes orother probes is correct. The images can also be used to verify that thetarget has not moved due to brain shift following opening of the skull.If the insertion cannulas or electrodes are not at target then a newtrajectory must be calculated so that the implanted electrodes arrive atthe true target. Once this is completed, the surgeon implants theelectrodes into the brain of the patient and verifies that implantedelectrodes are positioned at the target. The insertion cannulas andelectrodes can be advanced into the brain with use of robot with orwithout image guidance. This has been described for the introduction ofstereotactic electroencephalogram electrodes but another embodiment ofthe invention would be to control laser ablation of tumours or otherlesions.

The magnet mounted on the mover is preferably be able to rotate 180°about a vertical axis while inside the storage module so that thepatient end of the magnet always points towards the OR table in the roombeing serviced. Preferably the axis is stationary during the movementand located at or adjacent the center of the magnet, but it will beappreciated that the requirement is only that the magnet be rotated sothat the axis may not be fixed and may move as rotation occurs and theaxis may be located at one end or other location on the magnet.

The 3 key components of the magnet's ability to do 180° rotation are:

-   -   -a- Ultra Precise Mover Control: The left and right side tracks        are driven by servo motors which during rotation are engaged in        the opposite directions causing the magnet to do precise        rotation preferably while inside the storage module but in some        cases at other locations between the different operation        locations. Laser guided sensors are provided which detect any        variance from the required accurate rotation and provide motor        compensation to maintain accuracy. This allows the magnet to do        precise 180° rotation about a fixed vertical axis.    -   -b- Double Axis CC Design and Flex Tube Guidance which allows        the cable carrier to go left into a first operating room or        right into a second operating room and also to park in the        centre. The centre parked position is guided by a flexible tube        that articulates between two positions via a guided tack        assembly which has actuated pins that will lock the guide at the        different positions. By having the mover enter the required        selected room, the flexible tube naturally moves in that        direction until it stops at end of the curved track at which        point the flexible tube is locked by a controlled actuator pin.        The contour of the flex is determined by a fixed arced profile.        The flex tube must be locked to keep its curved position when        the magnet is traveling in the opposite direction back into the        storage module. Just before the magnet is fully inside the        storage module, the actuator locking pin releases which allows        the flex tube to straighten out and conform to the second        position.    -   -c- Slewing Ring Actuator Control: The Slewing ring mounted to        magnet has two parts where the bottom part is rigidly mounted to        the magnet and the top part is rigidly mounted to the cable        carrier bracket. The two sections of the slewing ring are locked        together at either 0° or 180°, or free to rotate by the slewing        ring actuator. To allow rotation, the top part is held locked or        engaged to the storage module via the actuator while the slewing        ring actuator is disengaged to allow magnet rotation. To allow        magnet travel, the module actuator is disengaged while the        slewing ring actuator is engaged.

The MRI system storage module accesses two adjacent rooms. It travelsbetween the rooms on the servo motor controlled tracked mover. Doors ateither side of the storage module allow access to one or the other ofthe rooms. An interlock is arranged such that only one door can be openat any time.

As explained above, rather than shield the whole room, localizedshielding is employed. This can be in the form of a shielding archmounted to the table where the localized RF shielding arch is a separatecomponent from the table and is stored in the storage module untilrequired. In the storage module the shield sits on a wheeled cart and isstored inside the storage module behind roll up doors on the front ofthe storage module. This wheeled cart also serves as an alignment/skullclamp positioning tool when preparing the patient for surgery. Thispositioning tool matches the magnet bore and allows the staff toposition the patient prior to surgery to ensure he/she will fit insidethe MR prior to it arriving. This will identify any patient to boreinterference and saves time when the magnet arrives. This is done aspart of patient preparation.

The cart has a fold down flap at its base that engages the front of thetable base and ensures the cart is aligned with the magnet travel. Thetable must be bolted to the floor via the two alignment screws at therear of the table. This arrangement therefore acts to locate the magnetas it is moved into position relative to the table with the guidance ofthe magnet movement ensuring that the magnet cannot move inaccuratelytoward the table with resultant potential collisions or inaccurate finallocation. The cart carries an alignment ring or bar which is movable onthe cart relative to the table.

The OR staff take the tethered bar and sweep the volume that representsthe location of the magnet bore when the bore is in place on the table.Any patient/skull clamp contact must result in repositioning of theskull clamp to clear the bar. If the patent clears the bar as it isrotated thus simulating the internal bore of the magnet, it clears theMR bore.

In accordance with another feature of the invention herein there isprovided an RF coil design for the intra-operative MRI arrangement.

The transmit coil can be provided as a conventional body coil locatedinside of the magnet at ISO-center with flare opening at the patientside of the magnet. It will generate quadrature uniform transmit RF B1field. This design can greatly reduce receive coil weight and improveworkflow. However the coils described hereinafter can be used for bothtransmit and receive functions. For head imaging, the receive coilcomprises an upper and lower coil design: The lower coil is thin-flexdesign which can be inserted between patient head and Head fixationDevice (HFD). The upper coil is Ultra-thin flexible coil which canimprove SNR by around 50%. The use of flexible conductors captured in athin flexible encapsulating materials which allow the structure to befully flexible to be draped over the face of the patient while lyingsubstantially in contact with all parts of the skin of the patientincluding forehead, cheeks and chin.

Both upper and lower coil can be integrated with the B0 shim coil whichcan further improve coil performance

To provide efficient sterilization of the coils for use in the surgicalenvironment, both the upper and lower coils can be manufactured so as tobe disposable with a disposable medical connector. Alternatively, thecoils may be of a reusable type but inserted into a sterilized bagduring use.

The coil design uses a plurality of, for example four, coil elementsarranged in a row with each partly overlapping the next. Adjacent coilelements 1 and 2, 2 and 3, 3 and 4 are decoupled by using the knownoverlap method obtained by the partial overlap together with theprovision of a shared capacitor coupling the two coil elements. Inaddition, next neighbor coil elements 1 and 3, 2 and 4 are alsodecoupled by using shared capacitors connecting the two next neighbourcoil elements, Previous coil decoupling only provides decoupling betweenthe adjacent coil element by using shared capacitors between them. Thereis no decoupling between next neighbor coil elements.

The required preamplifier can be put into a small box on the systemcable coupling the coils construction to the system. This allows thecoil construction itself to be very thin and lighter.

The differences of the present coil construction relative to previousdesigns of flex coil is as follows:

-   -   -a- the coil design provides effective decoupling between the        coil elements by the overlap, direct neighbour decoupling and        next neighbour decoupling;    -   -b- there is provided a cable connection making the coil        construction lighter to improve workflow;    -   -c- the preamplifier can be inside or outside the coil        construction making the coil very thin and therefore drapable    -   -d- the coil can be sterilized by being disposable of by using a        sterilized bag;    -   -e- the high flexibility and drape of the coil construction        causes the coil to lie closer to the patient and improve SNR up        to 50%.

The coil construction should have the following features:

-   -   it should not inhibit or restrict the placement and positioning        of the head skull to a head fixation device;    -   it should not restrict the use of navigation systems;    -   It should generate homogeneous RF field, with great sensitivity        inside the desired imaging volume;    -   it should not interfere or occupy the same space with the        designated surgical field;    -   it should generate a quadrature uniform transmit RF field        avoiding interference with the electronics of the surgical        robot;    -   it should control the pattern of specific absorption ratio (SAR)        deposition on the human head.    -   it should be able, by its drapability to be adjusted to a large        variety of human heads from a 6 month old infant to a 95% adult        male    -   it should, again by its high drapability, be easily integrated        with the Head fixation Device;    -   it should not disturb the sterile field by being easily        sterilized by disposal or by containment in a flexible bag or        the required dimensions;    -   in order to achieve higher SNR, the RF coil must as close to the        patient as possible again my use of high drapability

The Upper and lower coil size is 31 cm×22 cm. The total coil elements is8. This size is optimized for the penetration depth of reception fromthe patient head.

Traditionally, the upper coil is located on top of surgical drapewrapped around the patient head. While these are effective, they havesome disadvantages in that the upper RF coil is far away from thepatient, which could cause image SNR loses of around 40% to 50%. Thecoil cable is too long, heavy and very difficult to carry and operate.

According to further aspects of the invention which can be usedindependently of other features described or defined herein there isprovided:

The arrangement described herein can provide one or more of thefollowing advantages:

High Resolution State of the Art image quality.

Cryogen free 1.0 T Superconducting MRI.

No Helium with no quench line required.

Everything contained in one module which can be placed in most ORs:

No dedicated Control Room

No dedicated Equipment Room

Quick installation time—typically less than 3 weeks.

Localized RF shielding—no RF shield room required.

Module has a clean professional appearance with nominal 30 dB acousticattenuation when the doors are closed.

Includes portable MR compatible OR Table that adapts to the localized RFShield.

All system components including localized rf shield can be stored insidethe storage module so as to reduces OR clutter.

Magnet can be carried on a tracked crawler which distributes load over0.5 m2 floor area which minimizes floor loading.

BRIEF DESCRIPTION OF THE DRAWINGS

One embodiment of the invention will now be described in conjunctionwith the accompanying drawings in which:

FIG. 1 is an isometric view of an operating theater including anoperating table and an MRI imaging system according to the presentinvention, showing the magnet in a withdrawn position at one wall in theroom.

FIG. 2 is a similar isometric view of the same theater with the magnetin the imaging position.

FIG. 3 is a longitudinal cross-sectional view of the table and magnet inthe position of FIG. 2.

FIG. 4 is a transverse cross-sectional view of the table and magnet inthe position of FIG. 2.

FIG. 5 is a cross-sectional view similar to that of FIG. 3 on anenlarged scale showing the head clamp and RF transceiver.

FIG. 6 is an isometric view of an operating theater including a secondembodiment of magnet for an MRI imaging system magnet according to thepresent invention, showing the magnet moving into the room from astorage module.

FIGS. 7, 8, 9 and 10 are cross-sectional views showing the magnet ofFIG. 6 in different positions relative to an operating table enablingthe imaging system using the magnet and table to be used in a functionalimaging method where operations by the surgeon can be carried out usingboth ferromagnet and non-ferromagnetic tools.

FIG. 11 is an isometric view showing a transportation and alignment cartfor use with the table of FIG. 7 prior to the movement of the magnet upto the table.

FIG. 12 is an isometric view of the cart of FIG. 11 in a transportposition.

FIG. 13 is an elevational view of the magnet of FIG. 6 movable betweentwo operating rooms with a storage and operational module locatedtherebetween.

FIG. 14 is a plan view of the RF coil of FIG. 5 showing a series of coilloops connected to a communication cable for connection to the computercontrol system.

FIG. 15 is a cross-sectional view of the RF coil of FIG. 5 showing theRF coil in cross-sectional view.

FIGS. 16, 17 and 18 show a cable carrying system for use with the magnetof FIG. 6 in the rooms of FIG. 13.

In the drawings like characters of reference indicate correspondingparts in the different figures.

DETAILED DESCRIPTION

The apparatus for surgical procedures in the embodiment of the Figuresincludes an operating room 10 having a floor 11 and walls 12 containingan operating table 13 for receiving a patient for a surgical procedure.The table includes a table top 14 on which the patient lies and anupstanding support 15 which is typically adjustable to move the patientto a required position. Constructions of suitable tables are well knownin the prior art.

The table cooperates with a magnetic resonance imaging system 16 forobtaining images of a part of the patient at a series of times throughthe surgical procedure. The images are taken after part of the surgeryto assess progress in an analysis by the surgical team to allow thesurgical team to monitor the progress of the surgery.

The magnetic resonance imaging system 16 includes a magnet system 17comprising a cylindrical magnet 18 of magnet wire defining a cylindricalbore 19 within which a part of the patient is located for placementwithin high magnetic fields generated by the magnet. A control system21A is provided within the room inside a suitable container or storagemodule 21 at one side of the room. The control system operates the MRIsystem and includes a computer and display monitor for decoding anddisplaying the detected signals using computer operated programs fordecoding the various signals to generate images and for operating the RFsystem, the field of the magnet and other components conventional inthis type of system.

A radio frequency transmission and detection system 22 is shown in FIG.5 for eliciting and detecting from the part of the patient nuclearmagnetic resonance signals, in response to the magnetic field, includingan RF probe located adjacent to the head of the patient.

The magnet is mounted on a support system 23 mounting the magnet formovement relative to the table in a direction away from the first end 24of the table from a first position shown in FIG. 2 at or partly over thetable to a second position shown in FIG. 1 remote from the table. Thesecond portion is at one wall 12 so as to be well away from the table toensure the surgeon is not impeded by the presence of the magnet duringthe surgery.

Thus the first position of the magnet is arranged such that the head, orother part to be imaged, of the patient is positioned in the magneticfield of the magnet while the patient remains in place on the table.Thus the second position of the magnet is arranged such that the magnetis spaced from the first end of the table by a distance sufficient toallow the surgical team to move around the first end of table and toeach side of the table to access the patient and sufficient to allow toallow the surgical team to carry out the surgical procedure.

As set forth above, the magnet 17 is designed and arranged as a simpleconstruction of relatively light weight and small size to enable it tobe introduced into an existing operating theater and moved between thetwo positions within the room. Thus the magnet is dedicated solely tosurgery within the operating room and remains in the room when used in asingle room arrangement. A two room arrangement is described and shownhereinafter.

Thus the magnet has a bore of a small diameter of the order of 60 to 70cms and typically around 65 cms, so that it is of minimum total diameterthus reducing the length of wrapping wire required. This provides aweight of the order of 1 or 2 tonne, a width of the order of 4 to 5 feetand a length of the order of 5 to 7 feet defining a floor area in therange 15 to 35 sq feet and typically of the order of 20 sq ft.

This small dimension is assisted by the selection of a superconductingmaterial of a suitable material such as magnesium di-boride orNiobium-Tin or Niobium-Titanium which is superconducting at around orbelow 40 degrees absolute (Kelvin) and hence can be cooled by a coolingsystem to superconductivity without use of liquid helium.

That is a magnet 17 of this material is cooled by a vacuum cryo-coolingsystem 25 having a vacuum pump 26 driven by electricity where the pumpitself is cooled by a flow of cooling water. Arrangements of this typeare previously known to persons skilled in this art so that furtherexplanation is not required.

This weight and dimension of magnet allows the magnet to be carried onan air cushion support system 23 or track system described latersupported from the floor of a conventional operating theater applyingsuitable loads to the structure of the building without additionalstructural stiffening or supporting components. Thus a load of 2000 to4000 lbs can be spread over a floor area of 20 to 35 sq feet using anair cushion to spread the load without overloading the existing floorstructure. Alternatively the track system described below also can beused to spread the load.

The support system in one example thus comprises an air cushion formedin a chamber 27 covering the base area of the magnet and generated by afan 28 located within the magnet housing. The chamber has side skirts 29so as to contain the cushion within the chamber and so as to spread theweight over the entire base area.

The fan is associated with a suitable high efficiency filter system 29so that it expels and no particles into the chamber 27 so that nocontamination can be emitted from the side skirts.

In addition to the support system is guided from the first position tothe second position on guide rails 30 where wheels are guided along therails to ensure that the magnet properly moves between the twopositions.

A control processor 31 is provided on the magnet 17 which is operated inresponse to input controls from the control system 21A so that themagnet is arranged to be powered off to turn off the magnetic field whenin the second position. In this way the magnetic field is off during thesurgical procedures to avoid interfering with the surgeon's activitiesand is only turned on for imaging. Also the lift system fan 28 is alsooff as not required. At the same time, the magnet is arranged such thatthe cooling system pump 26 remains on powered by the electrical supply32 and the cooling water 33 from a wall connection 34 when the magneticfield is powered off. The water and electrical supplies are arranged sothat there is sufficient slack in the supply cables to allow movementbetween the first and second positions.

As shown in FIG. 5, the RF probe 22 comprises local transceiver RF coils36 so as, in some cases, to avoid use of a cylindrical body coil at thebore. These are of the type and construction described hereinafter toavoid the use of a body coil in the bore. These are arranged to wraparound the head clamp 37 and to drape over the head of the patient.

In order to avoid having to shield the whole room, there is provided ashielding structure 38 for excluding RF fields from the RF probe whichcomprises an arched elongate support frame 39 for extending over thepatient and supporting a shielding fabric or screen 40 extending fromoutside of the feet of the patient at the end of the table top 14 up tothe location 41 on the body which enters the bore. The fabric or screenthus forms an arched upper portion 42 over the patient and asemi-circular end portion 43 closing the end of the arched frame.

The shielding structure 22 further comprises a metal sheet 45 as part ofthe table top 14 located underneath the patient and extending across thetable to the sides of the shielding fabric or screen 40.

The shielding structure 22 comprises a cylindrical shielding layer 46inside the bore and a hinged door 47 on an end of the bore opposite thetable and containing a shielding layer 48.

All of the components of the shielding structure 22 are coupled togetherto form an integral shield fully surrounding the patient and the RFprobe.

The magnet is thus cryogen-free and will attain superconductivity (atless than 40K and nominal 39K) solely by the vacuum pump which requireswater cooling located on the magnet. This technology requires thecryocooler and the helium gas compressor which require water cooling.Advancements in vacuum pump technology, also known as a cryo-cooler,that achieves a partial vacuum at 39K which allows the superconductivityusing the wire of the material defined herein. No liquid helium isinvolved because there is no quench pipe to deal with the Liquid:Gasphase change.

The System and PDU cabinets are combined into a single cabinet. TheCabinets listed all have nominal 970 mm/37″ depths. This really is notan issue when considering new construction with a dedicated equipmentroom but when considering retrofits to existing hospitals, space is anissue and it may be necessary to put these cabinets in non-conventionallocations (e.g. hallways, viewing rooms, closets, etc). The cabinets canbe only 660 mm/26″ depth with all cabling out the top, nothing out theback. The approach is to have all cables out from the top. Since spacein a hospital is typically at a premium, all equipment to run the MRIsystem is located in a self-contained storage module of the order of 2m×4 m×3.2 m tall. The magnet mover cables, equipment and accessories areall located within the module as described in more detail herinafter.

There is a closed loop system with a water-to-water heat exchanger andan independent circulating pump inside the heat exchanger cabinet. Thereis a closed loop water cooling system with an inner heat exchanger.

There is a provision for city water bypass (to drain) inside thiscabinet but it could be done externally if space is at a premium. In theefforts to minimize external chiller installation costs, the system canuse direct hospital chilled water. The city water bypass is a riskmitigator in case the chiller goes down or is serviced. The city wateris acceptable for running the helium compressor (vacuum pump). But itcannot be a backup for cooling the gradient coil and gradient amplifier,both of which have a strict requirement of the cooling water such asdeionized water. Another option is to use direct hospital chilled waterusing an internal booster chiller.

The vacuum pump is also known as a cryo-cooler, the industry standarduses the term cryo-cooler, provides a pure vacuum at 0 K; which isalmost a vacuum at 3K).

A water-to-water heat exchanger has 2 isolated chambers with solidtransfer plates between chambers to do the conductive heat transfer. TheMR side of closed loop system always requires deionized water. Thechiller side has either chiller water or city water. It is necessary toavoid contamination between the two.

Cabinets require water cooling which is much quieter. Noise is always aconcern. The cabinets are in the equipment room or storage moduleseparated from the operator room. With a cryogen-free magnet a heliumcompressor is not required The system can compress the heat exchangerand put it in a small cabinet under the gradient amplifier cabinet. Thecryogen-free magnet still requires the helium compressor.

There is no conventional penetration panel. The cables for the most partgo directly from the storage module to the Magnet and are primarilycontained within the cabinet or module. There is a localized RF shieldaround the patient and inside the MR bore. There are waveguides and asmall penetration panel on the OR patient table that will have RFfilters associated with the Tx/Rx coils. It plugs directly into thissmall penetration panel. It requires the use of compact (DB9 sized) RFfilters and connectors or fibre optic cables through a waveguide. Thesystem has the all digital receiver design and fiber optic cables so itis not bulky even for a 16-channel system. The transmit cable is copper.

Conventional super conducting MR systems use a fixed cable tray betweenthe (fixed) MR and the equipment cabinets. The system uses a movingcable tray/carrier or Boom scheme to follow the magnet. The systemrequires nominal 12″/300 mm separation distance between the gradientcables and the RF cable. This is reduced by adding additional shieldingaround the gradient or RF cables. Also there are some fibre cables whichwill not be affected by the magnetic fields produced by the high powercopper gradient/RF cables. The system requires the large space betweengradient cables and RF cables. The system uses fiber cables and we haveextra shielding around the gradient cables. The cryogen-freesuper-conducting electromagnet can be turned on and off by the userrequiring roughly 15 minute field stabilization time. There should bemagnet charging cables available in addition to the gradient cables inorder to charge/discharge the magnet. The magnet charging cables arefixed to the magnet for frequent turn on and off. In the efforts ofminimizing cables, the gradients and charging cables are the same cablewith a programmable double-pole, single throw switch included dependingon the operating current of the magnet and the peak current required forthe gradient coil.

Conventional super conducting MR systems have cable sets selected as perthe location of the penetration panel (e.g. Siemens: 4 m before/16 mafter). They are also made up of cables chosen due to cost andperformance. The system herein uses a moveable magnet and needs the mostflexible cables available.

The system can in this embodiment us a non-ferrous air pallet thatglides around the OR. There is no problem carrying the weight. A 10 lbforce with push 5,000 lbs. The MR floor support to be nominal 2,000 lbswhich requires nominal 32 SCFM @ 30 PSI. Many manufacturers areavailable, for example Hoverair. For safety concerns, two people arerequired to move/steer the MR. Depending on the Cable management systemchosen, there are additional moment forces due to the stiffness of thecables that will have to be overcome.

Dust mitigation is obtained by adapting the pallet to include a skirtaround the perimeter that catches the exhaust and routes it through aHEPA filter. This would mitigate the OR contamination of dust beingblown off the floor. Air Supply is provided by a small rotary screwcompressor located above control cabinets which will supply air. Largevolume air is required with minimal noise has to be a priority. Thesystem uses an Accumulator (large storage tank) to provide a reserve.There is provided a wheel back up in case air supply fails. The magnetis bolted to this pallet.

There is provided a magnet/table engagement key since the magnet glidesaround the floor with little resistance so that the magnet cannot bumpinto the table including a physical “key” that mates/aligns themagnet/table together.

As an alternative, the magnet can have a motorized wheel mechanismassociated with a bottom frame. The MR typically sits against the rearwall. When required the user activates a pendent and moves the MRforward to mate with the table. The travel can be controlled by a limitswitch on the cable carrier. The alignment can follow a guide such astape on the floor or a stripe embedded in the flooring. The systemincludes a table to magnet engagement key to ensure proper tablealignment. This eliminates the need of an air supply with expensivescrew compressor, holding tank, and noise factor. The nurse does nothave to guide it into position. It drives itself with no dustmitigation.

The system has a modular concept where the magnet and cable carrier haveto be in the OR. The Equipment rack modules are placed in the OR orremotely located. The desire is to place this self-contained module intoany OR requiring a footprint of 4 m×2 m or in some cases 3.6 m×1.5 m and3 m tall as shown below. With the roll-up doors shut, the module will beas quite as possible. The overall control of the system is through theHMI (Human Machine Interface) which is located on the front of themodule. The standard outputs are to the hospital's DICOM/PACS system viathe internet or directly wired to the OR boom monitors. The standardinputs to the module are:

-   -   Electrical power (480V 3Ø)    -   Hospital Chilled water (supply and return)    -   City water (supply and drain)    -   Hospital Air (minor)

In regard to managing the cables between cabinets and magnet, there aretwo options:

Boom arm vs. rolling cable tray. Note that the cable management may adda moment force to the magnet transport solution which has to beovercome/managed. Also, we have to provide any additional shielding toadequately compensate for the required cable separation distances ifrequired.

Cable Carrier: This is mounted adjacent to the magnet and inside thestorage module and follow the magnet as it travels. While parked,everything is hidden inside the storage module. Limit switches on thecable carrier determine magnet position. 400 mm/16″ width is allottedfor this cable carrier.

The arched localized RF antenna system and RF Table Base Flange (RFpenetration panel) are in contact with the RF gasket. There is analignment key to make sure the magnet aligns with the table. The RFgasket also serves as an Anti-Collision Sensor that will stop themagnet's travel if a collision with the patient table/skull clampoccurs.

An MR compatible OR table is provided capable of accepting a MRcompatible Mayfield-like skull clamp with standard OR table features andsuitable for adaptation to a localized RF shield (see previous section).The table is of a non-ferrous metal beneath the removable archedlocalized RF antenna system which is pinned onto RF table base flangewhich is electrically isolated from the rest of the table. Two largewaveguides are included at the rear of the table to provide accessthrough the shield to the patient. Everything to the left that is theback section onwards of the localized RF antenna system, which mateswith the magnet, is non-ferrous plastic. The OR Table also has toservice non-neuro cases. The patient can lay on the table feet first orhead first. An extension is provided that allows the magnet to accessall parts of the body.

A spine board is provided which is a fiberglass rigid board that lays ontop of the table that allows non-neuro procedures to be performed. Thisprovides a distributed load over the entire table. A smaller spineextension can plug into holes for the skull clamp. Additional supportscan include side slides or a kick-down support floor pole. All weight ison the back section axis.

The table can have a sliding MR table surface which is more typically inkeeping with what a typical diagnostic table would do. Since the systemincludes a custom RF bore liner, this can include side rails which thetable slides on. This table surface is not moved during a OR surgerysince all the patient hook-ups have to move also which is too dangerous.The table is moved before the surgery starts and the hook-ups are inplace. Lift, Roll and Trendellenberg functions are present in the basesection of the table which are electrically isolated from the fiberglasssliding top section.

Part of the Neuro solution is to have a MR-Compatible Skull Clamp.Radiolucent Mayfield-style skull clamps are available off the shelf.They have been deemed not MR compatible since the carbon-fibre structureinduces eddy-currents in high field MR systems (>1.5 T). However, as thepresent system uses a magnet at around 1 tesla, so that anoff-the-shield carbon radiolucent skull clamp will work. This skullclamp is part of the RF Tx/Rx Head coil which has to fit around it.

Turning now to FIGS. 6 to 10, there is shown a modified embodiment usinga track mover. This includes a support system 50 supported from thefloor 51 mounting the magnet for movement relative to the table.

The support system comprises first and second endless drive tracks 52,53 each along or adjacent a respective side of the magnet and carried onan undercarriage 54 of the magnet. Each track is wrapped around endguide members 55, 56 and each has a lower track run 57 engaging thefloor. A drive

Each of the drive tracks is driven by a servo motor 59 driving through agear box 58 a sprocket 60 engaging the track. The servo motor avoids theuse of hydraulics and ensures very accurate control of the movement ofthe tracks. The servo motors are controlled by a drive system (notshown) so that when the drive tracks are driven simultaneously thisprovides accurate forward and rearward movement. When the tracks aredriven differentially this will provide a turning movement either tochange direction of movement or to rotate around a vertical axis. Thedrive system uses sensors 61 and 62 located on the undercarriage todetect a beam or line or mark, such as a laser beam generated by sources63 and 64 on the table at the floor 51 to direct the tracks to carry themagnet to a required location. When moving toward the table it isimportant that the magnet moves accurately along the line of the tableto avoid collisions with table or patient. Thus sensors on each side andat front and rear of the magnet ensure directional movement along therequired direction and immediately detects any deviation or twistingfrom a required path. In order to provide accurate guidance there are atleast two transversely spaced guide lines either at the floor or attable height which are detected by sensors at a front and rear of themagnet.

As described hereinafter, in the storage module, rotation of the magnetabout a fixed center vertical axis is obtained by driving the drivetracks in accurately opposed directions.

In one embodiment shown in FIG. 6 there is a single magnet mounted in asingle room 66 where the magnet retracts to a storage module 67 when notrequired. The storage module has a front open face which can be closedby a rolling door 68 when the magnet is stored.

Turning now to the arrangement in FIGS. 13 and 16 to 18 there areprovided two adjacent operating rooms 70 and 71 each having a floor andwalls containing an operating table (not shown) for receiving a patientfor a surgical procedure. Between the rooms is provided a storage module72 with roll doors 68 at each end for storing the magnet. The module 72is located between the rooms where the magnet is movable on its drivetracks or other transport system into the storage module 72 and from thestorage module to the table each of the rooms.

In order to service both rooms, the magnet is rotatable as shown at 73on the drive tracks in the storage module about a vertical axis 74 sothat a front end 75 of the magnet moves into the room at the forward endfor cooperating with the table.

As shown in FIGS. 16 to 18 there is provided a cable guide system 76which carries electrical and cooling water cables together with thesignal cables from the storage module 72 to the magnet. The cable guidesystem comprises a rolling support 77 which can move to an extendedposition shown in FIGS. 16 and 18 into the selected room and can roll orfold into a receptacle 79 which can be received into a receptacle 78defined by two parallel walls 79 and 80. The cable support thus remainsin a horizontal position extending generally from the top of the module72 to the top of the magnet as the magnet moves to carry the cables atthis horizontal position. The folding or rolling action allows the cablesupport to be retracted into the receptacle when the magnet is retractedinto the module. Underneath the outer end of the cable support at themagnet is provided a slew ring arrangement by which the rotation of themagnet in the storage module is accommodated. This combination ofextendible cable support and slew ring allows feeding of cables from thestorage module to the magnet when in each of the rooms and allows themagnet to rotate in the module between the rooms. The rotation of themagnet is driven by the tracks moving in opposite directions and theslew ring helps to maintain that movement accurately around the fixedvertical axis underneath the receptacle in the module.

The left and right side tracks are thus driven by servo motors whichduring rotation are engaged in the opposite directions causing themagnet to do precise rotation preferably while inside the storage modulebut in some cases at other locations between the different operationlocations. Laser guided sensors are provided which detect any variancefrom the required accurate rotation and provide motor compensation tomaintain accuracy. This allows the magnet to do precise 180° rotationabout a fixed vertical axis.

The cable carrying system is defined by the double axis CC design andflex tube guidance which allows the cable carrier to go left into afirst operating room or right into a second operating room and also topark in the centre. The centre parked position is guided by a flexibletube that articulates between two positions via a guided tack assemblywhich has actuated pins that will lock the guide at the differentpositions. By having the mover enter the required selected room, theflexible tube naturally moves in that direction until it stops at end ofthe curved track at which point the flexible tube is locked by acontrolled actuator pin. The contour of the flex in the cable guide asit rolls around into the receptacle is determined by a fixed arcedprofile 82. The cable guide which is rollable must be locked at theprofile 82 to keep its curved position when the magnet is traveling inthe opposite direction back into the storage module as the magnetmovement pushes against the cable carrier and forces it back into thereceptacle. Just before the magnet is fully inside the storage module,the actuator locking pin releases which allows the cable guide tostraighten out and conform to the second position.

The slew ring mounted between the magnet and the cable guide magnet hastwo parts where the bottom part is rigidly mounted to the magnet and thetop part is rigidly mounted to the cable carrier bracket. The twosections of the slew ring are locked together at either 0° or 180°, orfree to rotate by the slew ring actuator. To allow rotation, the toppart is held locked or engaged to the storage module via the actuatorwhile the slew ring actuator is disengaged to allow magnet rotation. Toallow magnet travel, the module actuator is disengaged while the slewring actuator is engaged.

The MRI system storage module thus accesses the two adjacent rooms. Ittravels between the two rooms on the servo motor controlled trackedmover. Doors 67 at either side of the storage module allow access to oneor the other of the rooms. An interlock is arranged such that only onedoor can be open at any time.

Turning now to FIGS. 11 and 12 there is shown an alignment device forproperly locating the patient on the table relative to the position ofthe cylindrical bore when the magnet is moved into its required locationat the table. Thus there is provided a location device for simulating alocation of a bore of the magnet when moved to the table. This is shownin stored position prior to use in FIG. 12 and in operating position inFIG. 11.

The location device comprises a movable cart 90 mounted on rear groundwheels 91 and on steerable front ground wheels 92 which can thus bemoved into position at the magnet. A locating system 93 comprisescooperating components 93A on the cart and 93B on the table which locatethe cart at the table in fixed predetermined position. The cart includesa folding extension portion 94 which can be retracted into storage asshown in FIG. 12. Thus with the base 15 of the table 13 fixed to thefloor by fastening components 15A and the cart fastened to the table bythe coupling 93, the cart is held fixed in position relative to thefloor so as to define a location for the magnet 16 to be brought up ontothe table.

The movable cart 90 provide a support base for receiving the shieldingassembly 38 previously described. Thus when not in use and not attachedto the table, the shielding structure can be moved to storage on thecart. The shielding structure carries an end guide ring arranged in useto butt up against the front face of the magnet when the magnet isbrought up to an imaging position. The ring 381 thus defines a firstguide ring which, when the shielding structure is attached to the tableas shown in FIG. 11, acts to simulate a location of the front end of thebore of the magnet when the magnet is in the first imaging position.

The cart carries a second guide ring 95 carried on rails 96 upstandingfrom the base of the cart. The cart is thus fixed relative to the tableand therefore relative to the ring 381 fixed on the table. The ring 95is fixed relative to the cart and thus relative to the table. The ring95 is located relative to the cart and thus the table so as to simulatea location of the rear end of the bore of the magnet when the magnet isin the first imaging position These two rings are therefore supported incoaxial position at relative locations which simulate the front and rearof the bore of the magnet when the magnet is brought to its imagingposition.

An elongate bar member 97 with a handle hole 98 and an inner edge 99 isprovided which has a length spanning the first and second guide rings.Each end has a shoulder 100, 101 sitting on an outside edge of therespective guide disk. The inside edge 99 of the bar is arranged so thatrotation of the elongate bar member 97 around the first and second ringsforms an imaginary cylindrical surface which accurately matches theactual cylindrical surface of the bore when the magnet is in the firstimaging position. Thus the inside edge of each of the rings matches thebore at its ends and the inside edge 99 follows the inside edge of therings so that the inside edge lies in the imaginary cylinder matchingthe bore at each position around the rings. Prior to the magnet beingbrought into position, with the patient and associated components suchas the head clamp and imaging coils in position on the table it will beappreciated that any impingement of the bar member on any part of thepatient or patient support predicts an unacceptable impingement of themagnet when the magnet is finally brought into imaging position. Thusthe bar acts as a prior detection system for ensuring the patientproperly positioned and if necessary repositioned, before the magnet isactually moved.

As explained above, rather than shield the whole room, localizedshielding is employed. This can be in the form of a shielding archmounted to the table where the localized RF shielding arch is a separatecomponent from the table and is stored in the storage module untilrequired. In the storage module the shield sits on the wheeled cart andis stored inside the storage module behind roll up doors on the front ofthe storage module. This wheeled cart also serves as an alignment/skullclamp positioning tool when preparing the patient for surgery. Thispositioning tool matches the magnet bore and allows the staff toposition the patient prior to surgery to ensure he/she will fit insidethe MR prior to it arriving. This will identify any patient to boreinterference and saves time when the magnet arrives. This is done aspart of patient preparation.

The cart 90 has a fold down flap 94 at its base that engages the frontof the table base and ensures the cart is aligned with the magnettravel. The table must be bolted to the floor via the two alignmentscrews 15A at the rear of the table. This arrangement therefore acts tolocate the magnet as it is moved into position relative to the tablewith the guidance of the magnet movement ensuring that the magnet cannotmove inaccurately toward the table with resultant potential collisionsor inaccurate final location. The cart carries an alignment ring or barwhich is movable on the cart relative to the table.

The OR staff take the tethered bar and sweep the volume that representsthe location of the magnet bore when the bore is in place on the table.Any patient/skull clamp contact must result in repositioning of theskull clamp to clear the bar. If the patent clears the bar as it isrotated thus simulating the internal bore of the magnet, it clears theMR bore.

The system can be used for imaging many parts of the body of the patientbut is primarily designed for imaging the head and when arranged to doso includes a conventional head clamp 37 with side pins 371 acting toclamp the head of the patient between the pins. The pins are carried ona bracket 372 attached to a support 373 mounted on an extension portion141 of the table top 14.

The coil construction 36 is best shown in FIGS. 14 and 15 and comprisesa lower RF coil assembly 361 mounted on or within the head clamp 37underneath the head of the patient. The lower coil 361 can be rigid orflexible and is preferably flexible to take up a required positionunderneath the head but on top of the bracket 371. If it is flexible itcan be moved to lie closely adjacent the lower part of the head. Thecoil construction can be of the same types and arrangement as the coilstructure of the top coil assembly 362 described below.

The RF probe comprises therefore the upper RF coil assembly 362 arrangedto be engaged with the head of the patient as shown in FIG. 15. Also inview of the fact that the coil remains in place during the surgicalprocedures, at least the RF upper coil assembly is in a sterilizedcondition allowing it to be used in the surgical procedure;

The sterilized RF upper coil assembly 362 is draped over the head of thepatient with the flexibility of the upper coil assembly causing it toconform at least in part to the shape of the parts of the head againstwhich the assembly is engaged. That is, the upper coil assembly isdraped into direct contact with the head of the patient and hassufficient flexibility so as to conform without application of forceholding it in place. The upper coil construction comprises a flexibleconductor arrangement 363 encapsulated in a flexible plastics material364 which directly engages the head of the patient and conforms thereto.Thus both the upper and lower surfaces of the coil are formed from theplastics material with the conductor contained within the material. Thematerial can be cast in place around a formed conductor assembly or canbe formed form two overlying layers containing the conductortherebetween. The flexible plastics material is formed from a materialwhich is MR compatible in that it can tolerate the magnetic field anddoes not create artifacts in the image. The flexible plastics material364 has a thickness less than 5.0 mm. The flexible plastics material hasa flexibility so that when applied over the head of the patient, edges365 of the upper coil depend below the head under their own weightwithout application of additional force.

In order to provide efficient sterilization for use in the surgicalprocedure, at least the upper coil assembly is manufactured so as to bedisposable and includes a disposable medical connector 366 forconnection to a signal cable 367 to the computer control system. Theconnector 366 includes a part at the end of the cable so that the cableis used repeatedly while the relatively minor component defined by theconductors 363, the covering plastics and the connector 366 are arrangedfor one time disposable use.

As an alternative, in order to provide efficient sterilization for usein the surgical procedure, at least the upper coil assembly 363 isinserted into a sterilized bag 368 during use for reuse of a previouslyused upper coil assembly. Each surgical procedure therefore uses aseparate sterilized bag into which the coil assembly 363 is insertedduring use.

The upper coil assembly 363 includes a preamplifier 369 which is mountedin a container 370 on the signal cable 367 connected to the computercontrol system so that the coil construction 363 itself is very thin andlight as the cable including the connector 366 and the preamplifier 369are not part of the draped conductor as shown in FIG. 15.

The preamplifier 367 includes for each conductor connected to arespective coil element 1, 2, 3 or 4 of the coil construction 363 arespective phase shift circuit 371 between the respective conductor 373and the respective preamplifier 372. Each conductor 373 is connected toa respective coil element 1, 2, 3, 4 by a respective inductor L1 to L4connected to the coil elements on the other end, with the values of thecomponents selected to make a phase shift for each coil element equal tohalf wave length at the working frequency of the MR system.

It has been found that the flexibility and drape of the upper coilassembly causes the coil to lie closer to the patient and improve SNR upto 50% and to allow it to be adjusted to a large variety of human headsfrom a 6 month old infant to an adult male.

The head transmit coil can be provided as a conventional body coillocated inside of the magnet at ISO-center with flare opening at thepatient side of the magnet. It will generate quadrature uniform transmitRF B1 field. This design can greatly reduce receive coil weight andimprove workflow. Alternatively the transmit function can be carried outusing the upper and lower coil construction 361, 362.

For head imaging, the receive coil comprises an upper and lower coildesign: The lower coil is thin-flex design which can be inserted betweenpatient head and Head fixation Device (HFD). The upper coil isUltra-thin flexible coil which can improve SNR by around 50%. The use offlexible conductors captured in a thin flexible encapsulating materialsallows the structure to be fully flexible to be draped over the face ofthe patient while lying substantially in contact with all parts of theskin of the patient including forehead, cheeks and chin.

Both upper and lower coil can be integrated with the B0 shim coil whichcan further improve coil performance

To provide efficient sterilization of the coils for use in the surgicalenvironment, both the upper and lower coils can be manufactured so as tobe disposable with a disposable medical connector. Alternatively, thecoils may be of a reusable type but inserted into a sterilized bagduring use.

As shown in FIG. 14, at least the upper coil assembly uses a pluralityof coil loops or elements 1, 2, 3 and 4 arranged in a row with eachpartly overlapping the next. This arrangement is generally known andused to provide decoupling between the individual coils.

That is, adjacent pairs of coil loops 1, 2 and 2, 3 etc are decoupled bythe partial overlap 1A, 2A etc together with a shared capacitor C2, C3coupling the two coil loops of the pair. Also next neighbor coil loops1, 3 and 2, 4 are also decoupled by using shared capacitors C20, C21connecting the two next neighbour coil loops.

In this way the upper coil assembly comprises at least first, second andthird coil loops 1, 2, 3 arranged in a row where each coil loop 1, 2, 3includes a plurality of capacitors at spaced positions therearound. Thuscoil 1 has capacitors C1, C2, C15 and C10. Coil 2 has capacitors C14,C7, C16 and C11 with each coil loop partly overlapping the next so thatthe first is partly overlapped with the second and the second is partlyoverlapped with the third;

Thus the first and second coil loops are decoupled by the partialoverlap thereof together with the provision of a first additionaldecoupling capacitor C2, C3 shared on a common portion of the first andsecond loops. Also the second and third coil loops 2, 3 are decoupled bythe partial overlap 2A thereof together with the provision of a secondadditional decoupling capacitor C3 shared on a common portion of thesecond and third loops. Finally, the first and third coil loops 1, 3 arealso decoupled by using third additional capacitor C20 in a connectingconductor 1B between the first and third coil loops. Also there isprovided a second connecting conductor 1C between the first and thirdloops.

As shown there is also provided a fourth coil loop 4 arranged in the rowwhere the third and fourth coil loops 3, 4 are decoupled by the partialoverlap thereof together with the provision of a third additionaldecoupling capacitor C4 shared on a common portion of the third andfourth loops and where the second and fourth coil loops 2, 4 are alsodecoupled by using fifth additional capacitor C21 in a connectingconductor 2A between second and fourth coil loops.

The coil design uses a plurality of, for example four, coil elementsarranged in a row with each partly overlapping the next. Adjacent coilelements 1 and 2, 2 and 3, 3 and 4 are decoupled by using the knownoverlap method obtained by the partial overlap together with theprovision of a shared capacitor coupling the two coil elements. Inaddition, next neighbor coil elements 1 and 3, 2 and 4 are alsodecoupled by using shared capacitors connecting the two next neighbourcoil elements, Previous coil decoupling only provides decoupling betweenthe adjacent coil element by using shared capacitors between them. Thereis no decoupling between next neighbor coil elements.

The arrangement herein as best shown in FIGS. 7 to 10 can be used in afunctional MRI operation where, in a first position shown in FIG. 7, thetable 13 and magnet 16 locate the head of the patient to be imaged onthe head clamp 37 within an imaging area 161 of the magnet and in asecond position shown in FIG. 9 the head of the patient is exposedbeyond a rear or remote end 751 of the magnet 16 so as to accessible foran operative procedure.

In order to move between these positions, the magnet and table aremounted for relative movement in a direction longitudinal of the tablefrom the first imaging position to the second non-imaging position;

As shown in FIG. 9, the magnet is movable along the table so that thepatient end is moved to a position closely adjacent a base of the tablewith the table cantilevered into the magnet and the table is extended bya slide portion 133 on a track 132 longitudinally into the magnet in thesecond position.

In the second position shown in FIG. 9, the magnet is powered off by acontrol 134 to turn off the magnetic field when in the second positionto enable surgical procedure to be carried out in the second positionusing ferromagnetic tools 135 such as drills.

After the part of the patient is exposed in the second position of FIG.9, the part is moved by the relative movement to the first position ofFIG. 7 for imaging and the power applied to the magnet by control 134,while non-ferromagnetic tools 137 are provided for additional surgicalprocedures to be carried out in the first position. The tools 137 caninclude a robot guidance system 136 within the magnet for carrying outthe additional surgical procedures. The tools 137 can include a probe atthe first position for insertion into the head of the patient guided bythe imaging such as for DBS.

For deep brain stimulation and other procedures on the brain performedby neurosurgeons, the magnet is powered down to zero field at FIG. 9 andthe system is moved so that the magnet is located over the chest and thestomach of the patient. This leaves the head of the patient exposedbeyond the end of the magnet remote from the table. The surgeon startsthe surgical procedures which require the use of ferromagnetic materialswhich are attracted to the magnet if at non-zero field. Typically, thisis used to form burr holes in the skull using drilling tools. Thus, thesurgeon can use conventional tools to carry out the conventionalsurgical procedures without danger from the attraction to the magnet.

When this part of the procedure is completed, the magnet is turned onand the surgeon can continue the procedure but using only MRI safedevices. The completion of these tasks requires supports in place forthe introduction of one or two insertion cannulas or electrodes throughthe burr holes which have been made in the patient's skull in the firstpart of the procedure. The trajectory of these are based on stereotacticimaging. When the magnet is at field, relative movement of the patientand magnet is provided such that the head of the patient is receivedinto the homogeneous field of view of the magnet. This can be obtainedby the longitudinal movement of the magnet along the table on its movingsystem. In an alternative embodiment, a telescopic component of thepatient table is moved to place the patient's head in the imaging fieldof view. Images are obtained and fused with pre-operative images whichmay contain anatomical, functional, and tractography information. Theseimages are used to verify that the trajectory for the electrodes orother probes is correct. The images can also be used to verify that thetarget has not moved due to brain shift following opening of the skull.If the insertion cannulas or electrodes are not at target then a newtrajectory must be calculated so that the implanted electrodes arrive atthe true target. Once this is completed, the surgeon implants theelectrodes into the brain of the patient and verifies that implantedelectrodes are positioned at the target. The insertion cannulas andelectrodes can be advanced into the brain with use of robot with orwithout image guidance. This has been described for the introduction ofstereotactic electroencephalogram electrodes but another embodiment ofthe invention would be to control laser ablation of tumours or otherlesions.

1. A method for imaging in surgical procedures comprising: providing anoperating room having a floor and walls containing an operating tablefor receiving a patient for a surgical procedure; mounting in the room amagnetic resonance imaging system for obtaining images of a part of thepatient at a series of times through the surgical procedure for analysisby the surgical team to allow the surgical team to monitor the progressof the surgery, the magnetic resonance imaging system comprising: amagnet system comprising a cylindrical magnet of magnet wire defining acylindrical bore within which a part of the patient is located forplacement within high magnetic fields generated by the magnet; a controlsystem for controlling and varying the magnetic fields; a radiofrequency transmission and detection system for eliciting and detectingfrom the part of the patient nuclear magnetic resonance signals, inresponse to the magnetic field, including an RF probe arranged to belocated adjacent to the part of the patient; and a computer and displaymonitor for decoding and displaying the detected signals; mounting themagnet for movement relative to the table in a direction longitudinal ofthe table from a first imaging position to a second non-imagingposition; wherein the magnet is powered off to turn off the magneticfield when in the second position; and wherein the magnet is cooled by acooling system which remains on when the magnetic field is powered off.2. The method according to claim 1 wherein the magnet wire is selectedfrom the group consisting of Magnesium di-Boride, Niobium-Tin andNiobium-Titanium.
 3. The method according to claim 1 wherein the magnetis cooled by a vacuum cryo-cooling system.
 4. The method according toclaim 1 wherein the magnet has a weight of less than 2 tonne and a floorarea in the range 15 to 40 sq feet and preferably of the order of 35 sqfeet.
 5. The method according to claim 1 wherein the magnet is carriedon a support system supported from the floor.
 6. The method according toclaim 1 wherein the magnet has a bore of a small diameter in the range60 to 70 cms and preferably or the order of 65 cms.
 7. The methodaccording to claim 7 wherein the magnet has a length in the range 5feet.
 8. The method according to claim 1 wherein the RF probe compriseslocal transceiver RF coils so as to avoid use of a cylindrical body coilat the bore.
 9. The method according to claim 1 wherein there isprovided a shielding assembly for excluding RF fields from the RF probewhich comprises a self-supporting arched structure for extending over atleast a portion of the patient and carrying a shielding material, thestructure extending from the feet up to the location on the body whichenters the bore.
 10. The method according to claim 9 wherein theshielding assembly comprises a portion of the shielding material as partof the table located underneath the patient and extending across thetable to the sides.
 11. The method according to claim 10 wherein theshielding assembly comprises a hinged door on an end of the boreopposite the table and containing a layer of the shielding material. 12.The method according to claim 10 wherein the shielding assemblycomprises a cylindrical shielding layer inside the bore.
 13. The methodaccording to claim 10 wherein the shielding assembly comprises a hingeddoor on an end of the bore opposite the table and containing a shieldinglayer.
 14. The method according to claim 1 wherein the magnet wire iscooled by a vacuum cryocooling system and wherein the only connectionsto the magnet system within the room comprise cooling water for thecryocooling system and electricity.
 15. The method according to claim 15wherein the water and electricity are maintained to the pump when themagnet is turned off.